Abstract. The biogenic volatile organic compound (BVOC) composition of ambient air at
a rural field site near Djougou, Benin has been studied as part of the AMMA
(African Monsoon Multidisciplinary Analysis) project. Ambient air was
sampled during day and night during the period 2 June 2006 to 13 June 2006.
Gas samples from within the forest canopy and from branch and cuvette
enclosure systems for four vegetation species were also obtained and
emissions flux estimates made. All samples were analysed for the presence of
isoprene, monoterpenes and sesquiterpenes by either gas chromatography-time
of flight mass spectrometry (GC-TOF/MS) or comprehensive gas
chromatography-time of flight mass spectrometry (GCxGC-TOF/MS).
Concentrations of isoprene ranged from a few tens of pptV to in excess of
3000 pptV. Similar concentration ranges for certain monoterpenes were also
observed. Limonene was seen at a maximum concentration in ambient air of
5000 pptV. The combination of leaf-level observations and direct analysis of
dried vegetation samples suggests that emissions of terpene species from
indigenous species are unlikely to account for the unexpectedly high ambient
concentrations of monoterpenes. Leaf scale emission measurements and
biological sample analysis indicated that \textit{Anacardium occidentale}, a non-native crop species found
throughout the tropics, was the dominant source of monoterpenes at this
location. These preliminary findings suggest that activities involving
species replacement have potential implications for the chemistry of the
African troposphere that have not been widely considered previously.